(1) Field of the Invention
This invention relates to processes used to manufacture semiconductor devices, and more specifically to processes used to create metal vias, used to interconnect metallization levels.
(2) Description of Prior Art
The semiconductor industry is continually attempting to provide the customer with higher performing silicon devices, while still maintaining, or even decreasing the cost of silicon chips. These objectives have been met by the semiconductor industry achieving micro-miniaturazation, or the ability to successfully create sub-micron device features. Significant advances in specific semiconductor fabrication disciplines, such as photolithography and dry etching, have allowed micro-miniaturazation to become reality. For example more sophisticated exposure cameras, as well as the development of more sensitive photoresist materials, have allowed sub-micron images in photoresist layers to be created. Similar advances in anisotropic, reactive ion etching, (RIE), has resulted in the sub-micron images in the overlying photoresist layer, being successfully defined in underlying materials, used for the fabrication of semiconductor devices.
However as specific features are reduced in size, several new concerns, not encountered with devices fabricated using less aggressive groundrules, are created. For example via holes in an interlevel dielectric material, used to interconnect metallization levels, when filled with a via metal, are difficult to properly fill due to the decreasing diameter of the via hole. The conformality of the depositing via metal decreases as the dimensions of the via hole shrink. Lack of metal in the via hole can result in significant reliability problems in terms of electromigration. In addition the narrower spaces between metal lines present problems when using standard insulator processes to fill these sub-micron spaces. The problems encountered with sub-micron features, namely the difficulty in filling narrow via holes with metal, as well as filling narrow spaces, between metal structures with insulator, have been addressed. For example Allman, et al, in U.S. Pat. No. 5,312,512, Fisher, et al, in U.S. Pat. No. 4,917,759, and Cote, et al, in U.S. Pat. No. 5,262,354, have described methods for creating narrow metal vias, as well as methods for insulator filling of narrow spaces between metal structures. However this invention will describe a fabrication process that offers a more complete solution to the sub-micron metal and insulator fill situation.